2.5 grams of 1-benzyl-5-hydroxy-3,4-dihydrocarbostyril and 0.48 g of 50% oily NaH are mixed with 30 ml of dimethyl formamide and stirred, then 4 g of 1-chloro-3-(4-phenylpiperazinyl)propane are added therein and warmed to 50°-60° C. for 2.5 hours. The reaction mixture is concentrated under a reduced pressure and the residue thus obtained is extracted with chloroform. After removing the chloroform by distillation, the thus obtained residue is recrystallized from ligroin to obtain 2.1 g of 1-benzyl-5-[3-(4-phenylpiperazinyl)-propoxy]-3,4-dihydrocarbostyril in the form of pale yellowish needle-like crystals with a melting point of 113° C.
